An air deflector is usually employed in conjunction with a windshield wiper, the latter generally comprising a wiper arm carrying a wiper blade, the function of the deflector being to divert air streams which impinge on the wiper blade when the vehicle on which the wiper is mounted is in motion at high speed, so as to prevent disengagement of the wiper blade from the surface being swept, which may occur due to the effect of aerodynamic forces generated by the air streams.
To this end, such a deflector should have its free edge directed towards the swept surface, which is of course in general the windshield of an automotive vehicle, this edge being arranged as close as possible to the swept surface in order to reduce to a minimum the space between the swept surface and the edge of the deflector. This is so that the air streams are prevented from being able to penetrate into this space in such a way as to give rise to a danger of setting up a lifting force on the deflector, such as to tend to raise it and thus to raise the windshield wiper to which it is connected.
This proximity of the edge of the deflector to the swept surface does however create a considerable problem due to the fact that windshields have, in practice, a large curvature, with this curvature developing in the direction of wiping movement of the windshield wiper, that is to say between a side edge of the windshield and its middle part.
One compromise solution has provided a cut-out on a deflector, such that it has a free edge with a curvature which corresponds to the mean curvature of the windshield of the vehicle. However, this solution has certain drawbacks during the wiping movement of the windshield wiper, and in particular at the ends of the wiping movement. What happens is that, towards the end of the sweep of the wiper, parts of the edge of the deflector at its extreme lateral ends become separated by a large amount from the swept surface, and this enables a large air flow to penetrate behind the deflector, thus setting up an aerodynamic force which tends to lift the blade. At the other end of the sweep, these portions of the deflector are brought very close to the swept surfaces, and a slight change in the air flow acting on the deflector can be sufficient to cause the latter to come into scraping contact with the surface, thus damaging the latter and eventually impeding good visibility by the driver.